1. Field of the Invention
The present invention relates to a steering controlling device for automobiles and so on.
2. Discussion of Background
In a conventional technique, an electric power steering device disclosed in Japanese Unexamined Patent Publication JP-A-7-76280 is known, wherein enhancement of an efficiency of power conversion is aimed. FIG. 5 is a block chart illustrating a structure of a conventional device. In the conventional electric power steering device, when a vehicle speed is low, it is judged that a load of a motor is high, whereby a voltage of power source is boosted, and the motor is driven by the boosted voltage.
However, since the conventional device is constructed as described above, the power source is boosted when a vehicle speed is low, whereby a frequency of using the converter is increased. Therefore, there are serious problems that an efficiency is lowered by a loss in the converter, a fuel consumption of a vehicle is deteriorated by over-discharge of a battery or an increment of generating power, and an effect of an electric power steering system, which is originally aimed to improve the fuel consumption by its high efficiency, is not obtainable.
Further, in the conventional device, failures of the converter are not considered.